Scout Now for Wheat Diseases

May 8, 2006

WOOSTER, Ohio -- Ohio's wheat is performing well, but now is the time for growers to start scouting for leaf diseases to continue keeping the crop in tip-top shape.

"The wheat is now between growth stages 7 (jointing) and 9 (full flag leaf emergence). This marks the beginning of the period during which we recommend that fields be scouted to determine which disease is present and at what level," said Pierce Paul, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center. "Although it has been a fairly dry spring up to this point, leaf diseases are beginning to show up on susceptible varieties in some fields."

Stagonospora leaf and glume blotch, powdery mildew and leaf rust are three of the most problematic leaf diseases for wheat. But if identified early enough they can be easily controlled with fungicides to limit yield losses.

"Powdery mildew is showing up now in some fields and the time is right for Stagonospora," said Paul, who also holds an Ohio State University Extension appointment. "The decision to apply fungicides is based on the level of disease, which diseases are occurring, the varieties that have been planted and potential yield impacts. Scouting is necessary to make these determinations and growers need to get off their tractors and into their fields to do it properly."

To properly scout fields, Paul recommends that growers collect between 30 and 50 plants randomly throughout a field and look for lesions on the lower leaves and leaf sheaths and the leaf just below the flag leaf.

"Two to three lesions on the leaf just below the flag leaf is considered threshold and a fungicide application may be warranted if the variety is susceptible," said Paul. "It's important to keep the disease from spreading to the flag leaf and other top portions of the wheat crop because the top leaves and the head contribute most of the sugar for grain development. Yield losses are greatest when the upper two leaves of the plants become diseased at or before heading. When this happens, yield losses can be as high as 25 to 30 percent."

Stagonospora leaf and glume blotch is most severe in wet weather from mid-May through June and in temperatures ranging between 68 degrees and 80 degrees Fahrenheit. The disease is characterized by lens-shaped, chocolate-brown lesions with yellow borders. Powdery mildew spreads during conditions of high humidity and is characterized by powdery white mold growth on leaf surfaces. In most years, leaf rust is detected in the state after flowering of the crop and is usually considered too late to cause significant yield loss.

Several fungicides are available for use on wheat. If powdery mildew is the target disease then Tilt or PropiMax should be applied. Tilt, PropiMax, Quadris, Quilt, Stratego, and Headline have good effectiveness against Stagonospora leaf blotch, other leaf blotch diseases and leaf rust.

Wheat growers should also begin preparing for the potential arrival of Fusarium head scab, and the Fusarium Head Blight Prediction Center is now up and running to assist in tracking disease developments. The Web-based forecasting model (http://www.wheatscab.psu.edu) serves 23 states, including Ohio. It uses flowering dates of the wheat crop, along with weather conditions, to assess the risk of head scab. The site is maintained by OSU Extension, Penn State University, North Dakota State University, Purdue University and South Dakota State University.

Wheat in Ohio generally enters flowering stage sometime in May.

Author(s): 
Candace Pollock
Source(s): 
Pierce Paul